Brush for high intensity arc searchlights



July 26, 1 938. J. F. PETERS ,1

BRUSH FOR HIGH INTENSITY ARC SEARCHLIGHTS Filed Feb. 27, 1937 John FDefers.

Patented July 26, 1938 BRUSH FOR HIGH INTENSITY ARC SEARCH- LIGHTS JohnF. Peters, Edgewood, Pa., assignor to Westinghouse Electric &Manufacturing Company, East Pittsburgh, Pa., a corporation ofPennsylvama Application February 2'7, 1937, Serial No. 128,202

13 Claims.

My invention relates to are searchlights and more particularly to thebrushes used to conduct current to the electrodes of such searchlights.

In the operation of arc searchlights, it is common practice to feed theelectrodes to the are as they are consumed in the are by moving theelectrodes, which are usually round rods, toward the arc in thedirection of their axes. In addition to the longitudinal motion, theelectrodes,

and particularly the positive electrode, are rotated about their axes tosecure even consumption of the electrode in the arc. Because of therelative motion of the electrode and the electrode holder, or electrodehead as it is sometimes called,

it is necessary that contact brushes be mounted on the head to bear uponthe electrode to conduct current thereto while the arc is burning.

High intensity searchlights such as operate on ciu'rents of from 150 to250 amperes require that Lt. very good contact be maintained between thebrush and the electrode to prevent excessive arcing and resultantburning of the brush. Poor contact between the brush and the electrodecauses considerable power loss and voltage drop between the brush andelectrode. Such power loss causes heating of the brush which in turncauses pitting and deterioration of the brush. Such pitting furtherincreases the contact resistance between brush and electrode and so thecondition is aggravated until it is necessary to replace the brush orrefinish its contact surface. Pitting of the brush surfacealso'increases the sliding frictional resistance between the brush andthe electrode thus placing an excessive burden upon the electrodefeeding mechanism.

The contact surface of the brushes in common use heretofore has been inthe form of a cylindrical surface intended to cover the electrodesurface. It has been found that the diameters of 40 the electrodes varyboth as between electrodes and in the individual electrodes. It isapparent that, in order to permit the brush contact surface to cooperatewith all electrode diameters, it is necessary that the diameter of thebrush con- AS tact surface be made at least as large as the largestelectrode diameter that is likely to be encountered.

As a result of the construction just described, single line contactexists between the brush and the electrode except when the maximumdiameter of electrode is engaged by the brush. This means that only linecontact exists between the brush and the electrode. As a result a highcontact resistance exists, causing the brush to pit 5 excessively andnecessitating frequent reaming Cir of the brush contact surface. Thisrepeated reaming shortens the brush life and causes excessivereplacement and maintenance costs.

The object of my invention is to provide a brush for use with theelectrodes of an arc searchlight which shall have a lower contactresistance than brushes now employed.

Another object of my invention is to provide a brush for use with theelectrode of an arc searchlight which shall have its contact surface soshaped as to provide a plurality of line contacts between the brush andthe electrode.

A further object of my invention is to provide a brush for use with theelectrodes of an arc searchlight which shall have its contact surface soshaped as to minimize the contact resistance between the brush and theelectrode.

A still further object of my invention is to provide a brush for usewith the electrode of an arc searchlight which shall have its contactsurface so shaped as to minimize the heat generated and consequentpitting at the brush contact surface.

Another object of my invention is to provide a brush for use with theelectrode of an are search light which shall have its contact surface soshaped as to prolong the life of the brush thus obtaining increasedmaintenance and replacement economies.

Another object of my invention is to provide a brush for use with theelectrode of an are search.- light which shall have its contact surfaceso formed as to provide two line contacts between the brush and theelectrode thus insuring that the electrode be held securely againstlateral movement.

Another object of my invention is to so shape the contacting surface ofa brush for the electrode as to obtain a high contact pressure per unitof contact surface and to thus provide a better conducting contactbetween the brush and electrode.

These and other objects of my invention will be apparent after readingthe following detailed description in connection with the accompanyingdrawing, in which Figure 1 is a diagrammatic illustration of theelectrodes and electrode feeding mechanisms of an arc lamp with thebrushes in their cooperative relationships.

Fig. 2 is an end elevational view showing the contact relation betweenan electrode and a brush which has a cylindrical contact surface.

Fig. 3 is an end elevational view showing the contact relation betweenan electrode and a brush embodying the principles of my invention.

the best results.

Fig. 4 is a perspective View of the brush shown in Fig. 3; and,

Figs. 5 and 6 illustrate the contact relation between an electrode andmodified forms of brushes embodying my invention.

In carrying out my invention, I have provided on the arc head unit ofa'searchlight, a pair of brushes with V-shaped slots in that end of thebrushes which bears on the electrode, with the slots runninglongitudinally of the electrode and each side of the slot contacting theelectrode.

Referring to Fig. 1, I have illustrated the positive and negativeelectrodes i and 2 of an arc Searchlight with the mechanism for feedingthe electrodes to the are 3 and 4, and the mechanism 5 for rotating thepositive electrode, these feeding and rotating mechanisms being drivenby a constantly rotating motor 6 through suitable gearing. Power forenergizing the arc is supplied to the electrodes through brushes 1 andthese brushes are energized from a suitable power source, asillustrated.

It is understood that this mechanism is only illustrative and thegearing mechanisms are not drawn to scale. The mechanism for rotatingthe positive electrode is provided to insure even burning of thepositive electrode. The mechanism for feeding the electrodes to the areare provided to compensate for the consumption of electrodes in the arcand to maintain the arcing tips in a fixed position.

It will be seen that the positive electrode has both a rotational and asliding movement relative to its brushes. In Fig. 2, I have shown theusual form of brush contact surface. Heretofore, this has been acylindrical surface and because of the variation in the diameter of theelectrode along its length and the variation in diameter as betweenelectrodes it is apparent that a brush surface diameter could not bechosen that would fit all electrodes, that the surface diameter wouldhave to be at least as large as the largest expected electrode diameter,that electrode diameter in most cases would be smaller than the brushsurface diameter and that contact between the brush and the electrodewould be only line contact at the point A.

Furthermore, the cylindrical contact surface of the brush might varyfrom line contact to surface contact depending on the relative diametersof the brush surface and the electrode. This gives a variation incontact pressure between the brush and the electrode and as this contactmore nearly approaches the surface contact, there is not sufficient unitpressure between these surfaces to insure good conduction between thebrush and the electrode.

For these reasons, it was necessary that as near as possible to linecontact be maintained between the brush and the electrode at all times.This line contact is obtained by providing the brush shown in Fig. 3.This brush has a V-shaped slot lengthwise of the brush and the electrodefits into this slot, as illustrated. Such an arrangement provides linecontact between the brush and electrode at the two points B, thusinsuring high unit pressure between the brush and electrode andproviding two of these high pressure contact surfaces.

The angle between the sides of this V-shaped slot shown in Fig. 3 may betaken as merely illustrative of the principle of this invention and isnot necessarily the exact angle which will give The angle for obtainingthe best results would probably vary with the diameter of the electrodeto be used with the brush and such angle would have to be determined byexperiment.

If it should be desirable to increase or decrease the brush contactpressure above or below that obtained by the plane surfaces of theV-shaped slot shown in Fig. 3, the V-shaped slot may have side surfaceswhich are convex or concave as illustrated in Figs. 5 and 6. It will benoted that the same principles apply in these modifications, that linecontact is obtained between the brush and electrode at two separatedpositions on the electrode and that the contact of the two sides of theV-shaped slot with the electrode serves to maintain the electrode at afixed position and prevent lateral movement of the electrode.

Experimentation and use in practice have shown that the shaping of thebrush contact surface after the manner illustrated and described hasprolonged the life of the brushes and has made it necessary to refinishthe contact surfaces of the brushes less often than when the cylindricalcontact surface illustrated in Fig. 2 is used. It has also been foundthat the centering effect of the V-shaped contact surface on theelectrode has resulted in a better beam projected from the Searchlight,since the variations in the beam intensity and focus have beeneliminated by preventing lateral movement of the electrode.

In compliance with the requirements of the patent statutes, I have shownand described herein a preferred embodiment of my invention. It isunderstood, however, that the invention is not limited to the preciseconstruction shown and described, but is capable of modification by oneskilled in the art, the embodiments herein shown being merelyillustrative of the principles of my invention.

I claim as my invention:

1. In an arcing device in which the electrode is rotated about its axisand is moved axially to feed it to the are, means for conducting currentto the electrode comprising a fixed brush having a V-shaped slot, thesides of the slot serving as the contact surfaces between the brush andthe electrode.

2. In a brush for conducting current to an electrode of an are, whichelectrode rotates and is moved into the arc, said brush being so formedas to maintain substantially line contact with the electrode at aplurality of circumferentially spaced positions on the electrode.

3. In an arc Searchlight having means for rotating an electrode andfeeding the electrode to the are, a fixed brush for conducting currentto the electrode, said brush being so formed as to provide a pluralityof surfaces in different planes as surfaces of contact with theelectrode.

4. In a means for maintaining electrical contact with a substantiallycylindrical surface which rotates about its axis and which moves in thedirection of its axis, a brush made of conducting material and having aslot in one side thereof, said slot being so formed that, when the brushis placed in contact with said cylindrical surface, with the cylindricalsurface lying in the slot, each of the slot surfaces will maintainsubstantially line contact with the cylindrical surface.

5. In a device for maintaining electrical contact with a body having asubstantially cylindrical surface which has a motion in the direction ofits axis and rotation about its axis and Whose dimensions may lackuniformity, a brush made of conducting material and having a slot soshaped that each of its surfaces acts as a contact surface between thebrush and said body.

6. In a device for maintaining electrical contact with a body having asubstantially cylindrical surface which has a rotational movement aboutits axis and a movement in the direction of its axis and whosedimensions may vary from point to point along the length of the body, abrush made of conducting material and having a V- shaped slot, the sidesof the slot being curved and serving as the contact surfaces between thebrush and the bodies.

'7. In a device for maintaining electrical contact with the electrodesof an electric arc, which electrodes are rotated about their axes andmoved in the direction of their axes, are substantially circular incross section and may vary in dimensions, cross sectional shape anddegree of straightness both as between points along the individualelectrodes and as between electrodes, a brush made of conductingmaterial and having a slot with curved sides, said slot being sodisposed that its sides form contact surfaces between the brush and theelectrode.

8. In an arcing device having an electrode which is rotated and fed tothe are as it is consumed in the arc, a brush for conducting current tosaid electrode, said brush having a surface for contacting the electrodewhich comprises a V-shaped slot having sides which are plane surfaces.

9. In an arcing device having an electrode which is rotated and fed tothe arc, a brush for conducting current to the said electrode, saidbrush having a contact surface in the form of a V-shaped slot whosesides are curved surfaces.

10. In an arcing device having an electrode which is rotated and fed tothe arc, a brush for conducting current to the said electrode, saidbrush having a contact surface in the form of a V-shaped slot whosesides are convex.

11. In an arcing device having an electrode which is rotated and fed tothe arc, a brush for conducting current to the said electrode, saidbrush having a contact surface in the form of a V-shaped slot whosesides are concave.

12. In an arcing device in which an electrode of substantially circularcross-section is rotated about its axis and is moved axially to feed itto the arc, means for conducting current to the moving electrodecomprising a fixed brush bearing against the electrode, said brushhaving a V-shaped slot, the sides of said slot serving as contactsurfaces between said brush and the electrode.

13. In an arcing device having an electrode which is rotated and fed tothe arc, a brush for conducting current to the electrode, said brushhaving a contact surface in the form of a V- shaped slot whose sides aresurfaces generated by the movement of a substantially straight linewhile maintaining the line parallel to a predetermined line.

JOHN F. PETERS.

